Temperature-stable non-magnetic alloy

ABSTRACT

An alloy composed of nickel, boron and phosphorus that does not change substantially in magnetic properties, hardness or resistivity, with substantial changes in temperature.

This is a division of application Ser. No. 387,601, filed Aug. 13, 1973now abandoned.

BACKGROUND OF THE INVENTION

One type of magnetic storage medium is known as a magnetic memory disc.In general, this article comprises a substrate disc of non-magneticmaterial, a thin film of a magnetic material, a surface layer of a hardsubstance to protect the magnetic film from damage and, often a thinsurface film of a lubricant. The substrate material usually used inmagnetic memory discs is any of several aluminum alloys. Aluminum ispreferred for this purpose because of properties such as lightness,strength and resistance to moderately high temperatures. A suitablealloy is one containing 5.1- 6.1% zinc, 2.1- 2.8% magnesium, 1.2- 2%copper, 0.18- 0.4% chromium and the balance aluminum.

One type of magnetic film commonly used in magnetic memory discs iscomposed of a cobalt-phosphorus alloy because of its desirable magneticproperties. The magnetic material should be one that can be deposited asa thin film since thin films are conducive to obtaining high packingdensity of stored information.

However, it is not feasible to deposit the cobalt alloy directly uponthe aluminum alloy substrate because the cobalt alloy must be depositedon a smooth, highly polished surface. The aluminum surface is too roughand cannot be made to take a sufficiently high surface polish for thispurpose.

To provide a highly polished surface of non-magnetic material suitablefor deposition of the cobalt alloy film, a relatively thick (about onemil) layer of non-magnetic nickel-phosphorus alloy is deposited on thealuminum alloy substrate and this layer is then given a high polish.

The magnetic cobalt alloy film is then deposited on thenickel-phosphorus alloy layer. It is important that the cobalt alloylayer be protected from all surface damage since any surface damage canresult in loss of parts of the recorded information.

Layers of various protective materials such as plastics, or metals suchas rhodium, have been tried to protect the cobalt alloy layer fromsurface damage. Rhodium has desirable physical characteristics for thispurpose but it is deposited from an acid solution that attacks thecobalt alloy layer. In seeking a better protective material that is notdetrimental to the cobalt alloy layer, a layer of cobalt oxides has beenproposed. Cobalt oxides are hard enough, adherent enough and otherwisehave suitable properties for the intended purpose. However, the layer ofcobalt oxides is formed by heating the deposited cobalt alloy layer at atemperature of about 210° - 290°C under controlled humidity conditions.At these temperatures, the underlying non-magnetic nickel-phosphoruslayer becomes magnetic and this undesirably affects the magneticproperties of the cobalt alloy layers as a storage medium.

It would be desirable to have an otherwise suitable non-magnetic layerbeneath the cobalt alloy layer that does not become magnetic at thetemperatures used to form a cobalt oxide layer from cobalt. It wouldalso be desirable to have such a layer that can be deposited by aninexpensive electroless deposition process rather than one requiring amore expensive process such as evaporation or sputtering.

One of the many other uses for electrolessly deposited nickel-phosphoruslayers is for resistors in "thin" film hybrid circuits or for resistorsin read-only memory matrix applications. Resistors having a rather widerange of resistances can be prepared by this method and the resistors soproduced can be made to have small temperature coefficients ofresistance depending upon conditions of deposition. However, in thepast, it has been found that a heat treatment of these nickel-phosphorusfilms at temperatures of about 150° to 250° C for from 1 to 15 hours isnecessary to stabilize both the resistances and the temperaturecoefficients of these resistors. It would be desirable to be able toeliminate the need for the heat treatment.

The present invention is based on the discovery that certain alloys ofnickel, phosphorus and boron have properties which make these materialsespecially suitable for the non-magnetic layer beneath the magneticcobalt layer in a memory disc and also cause these alloys to beparticularly attractive for film type resistors in hybrid electroniccircuits. Non-magnetic alloys containing about 0.1 to about 0.7 wt.percent boron, about 6-16 wt. percent phosphorus and the balance nickelhave been found to remain substantially non-magnetic when heat treated.Alloys containing 0.1 to 0.7 wt. percent boron, 5 to 16 wt. percentphosphorus and the balance nickel have been found to have lowertemperature coefficients of resistivity than either alloys containingonly nickel and phosphorus or alloys containing only nickel and boron.

THE DRAWING

FIG. 1 is a cross section view of part of a magnetic storage element inaccordance with the present invention;

FIG. 2 is a cross section view of a film type resistor in accordancewith the invention; and

FIG. 3 is a graph comparing percent changes in resistivity versustemperature of an alloy coating of the present invention with certainprior art alloys.

DESCRIPTION OF PREFERRED EMBODIMENTS EXAMPLE 1

A magnetic storage element, in accordance with the present invention, isillustrated in FIG. 1. This storage element may comprise an aluminumalloy substrate disc 2, (a small portion of which is indicated inFIG. 1) a layer 4 of a non-magnetic nickel-phosphorus-boron alloy havinga polished upper surface 6, a thin layer of cobalt-phosphorus alloy 8and a thin top layer 10 of cobalt oxides.

In order to prepare one side of the aluminum disc 2 to receive thenickel alloy coating 4, that side is cleaned and degreased by treatingit with an aqueous solution containing 10% by wt. NaOH and 5% by wt.NaF. This solution is then thoroughly rinsed off and the aluminumsurface is treated with an aqueous solution containing 50% by volumeconcentrated nitric acid. The nitric acid solution is also then rinsedaway.

A very thin layer of zinc (not shown) is then deposited on the cleanedaluminum surface by treating the surface with an aqueous solutioncontaining about 455 g/liter of NaOH and about 83 g/liter of ZnO. Thesetwo ingredients react to form sodium zincate which is then reduced tozinc.

In order to deposit a coating of nickel-phosphorus-boron alloy on thezinc coating, the article is immersed in a bath having the followingcomposition:

    Ni.sup.+.sup.+ (from a nickel sulfamate concentrate)                                                   8.9 × 10.sup..sup.-2 M                         NaH.sub.2 PO.sub.2.H.sub.2 O                                                                           2.35 × 10.sup..sup.-1 M                        HCO.sub.2 Na             0.5M                                                 (CH.sub.3).sub.2 NHBH.sub.3                                                                            4.23 × 10.sup..sup.-2 M                        pH                       4.0                                                  Temperature              75°C                                      

The alloy coating deposited from the above bath is composed of 10.2 wt.% phosphorus, 0.52 wt. % boron and the balance nickel.

A coating 8 of a magnetic cobalt-phosphorus alloy is then deposited onthe top surface 6 of the nickel-phosphorus-boron alloy coating 4. Thiscoating may be deposited by immersing the substrate in the followingbath:

    CoCl.sub.2.6H.sub.2 O                                                                            7.5      g/liter                                           H.sub.3 C.sub. 6 H.sub.5 O.sub.7.H.sub.2 O (citric acid)                                         19.0     g/liter                                           NH.sub.4 Cl        12.5     g/liter                                           NaH.sub.2 PO.sub.2.H.sub.2 O                                                                     10.0     g/liter                                           pH (with NaOH)     8.2                                                    

This bath is operated at 80° C.

The cobalt alloy films may be about 5000 A thick, for example.

To provide a hard protective coating over the cobalt alloy film 8, asurface portion of the film 8 is converted to cobalt oxides by heatingin moist air (relative humidity about 60%) at temperatures between about210° and 290° C. Within this temperature range, thenickel-phosphorus-boron layer 4 remains substantially non-magnetic. Incontrast, a nickel-phosphorus alloy layer containing about 10%phosphorus does become magnetic at temperatures of about 290° C and itsmagnetic properties adversely affect the magnetic properties of anadjacent cobalt-phosphorus layer

EXAMPLE 2

Thin layers of nickel-phosphorus-boron alloys on ceramic or othersubstrates are also useful as resistors in hybrid microelectroniccircuits. An article of this nature is illustrated in FIG. 2 which showsa ceramic substrate plate 12, which may be a high alumina ceramic, forexample, on the top surface of which is a film 14 of anickel-phosphorus-boron alloy. The film 14 comprises a resistor whichmay be connected into a circuit containing a pattern of conductors andother circuit components (not shown) on the same ceramic substrate.

A preferred method of depositing the film 14 of nickel-phosphorus-boronalloy on the ceramic substrate 12 is electroless deposition. Sinceceramic substrates are not catalytic to electroless deposition ofmetals, the ceramic surface must first be sensitized by treating it witha sensitizer such as a dilute solution of stannous chloride acidifiedwith hyrochloric acid and then activated by treating the sensitizedsurface with a substance such as a solution of palladium chloride. Boththe sensitizing and the activation procedures are conventional in theart.

A coating of nickel-phosphorus-boron alloy may then be deposited on thesensitized and activated surface using the same bath as used in theexample above. The thickness of the coating may be about 1500 A, forexample. One way to obtain a resistor of defined area is to deposit anoverall coating of the alloy and then by depositing a layer ofphotoresist, exposing and etching (with 50% nitric acid, for example),remove all of the alloy film except the areas desired for the resistoror resistors.

A comparison between a film of a nickel-phosphorus alloy, a film of anickel-boron alloy and a film of a nickel-phosphorus-boron alloy, withregard to resistivity change with changes in temperature, is shown inthe graph of FIG. 3. In this Figure, curve A is for a film consisting of10% by wt. phosphorus and the balance nickel. Curve B is for a filmconsisting of 0.5% boron and the balance nickel. Curve C is for a filmconsisting of 0.52% boron, 10.2% phosphorus and the balance nickel.These were films which had been deposited on ceramic substrates.

The resistivity of each of these films was first measured at ordinaryroom temperature. The films were then given heat treatments of 15minutes in an atmosphere comprising 10% hydrogen and 90% nitrogen at aseries of temperatures between room temperature and 450° C. The filmswere permitted to cool after each heat treatment. Resistivities of thecool films were measured after each heat treatment and the percentchange in resistivity (in ohms per square) as a function of temperaturewas plotted for each film. The plotted data indicate that the percentchange in resistivity for the nickel-phosphorus-boron film (curve C) wasnegligible up to a temperature of about 300° C, whereas the percentchange in resistivity at 300° C for the other two films was much higher.

The following are examples of how to deposit films ofnickel-phosphorus-boron alloys containing various percentages ofphosphorus and boron. In all cases the source of the nickel was asulfamate concentrate. All of these films were heat treated as inExample 2 and all of them had a stable resistivity at temperatures up toabout 300° C. Also, all of them showed little or no change in magneticproperties at temperatures up to about 300° C.

    ______________________________________                                        Example 3                                                                     ______________________________________                                        Ni               8.9 × 10.sup..sup.-2 M                                 NaH.sub.2 PO.sub.2                                                                             9.5 × 10.sup..sup.-2 M                                 Dimethylamineborane                                                                            4.2 × 10.sup..sup.-2 M                                 HCO.sub.2 Na     5 × 10.sup..sup.-1 M                                   pH               5.5                                                          Temperature      60°C                                                  % P              5.33                                                         % B              0.45                                                         Example 4                                                                     ______________________________________                                        Ni               8.9 × 10.sup..sup.-2 M                                 NaH.sub.2 PO.sub.2                                                                             1.4 × 10.sup..sup.-1 M                                 Dimethylamineborane                                                                            4.2 × 10.sup..sup.-2 M                                 HCO.sub.2 Na     5 × 10.sup..sup.-1 M                                   pH               5.0                                                          Temperature      60.0°C                                                % P              9.88                                                         % B              0.47                                                         Example 5                                                                     ______________________________________                                        Ni (as metal)    8.9 × 10.sup..sup.-2 M (sulfamate)                     NaH.sub.2 PO.sub.2                                                                             1.9 × 10.sup..sup.-1 M                                 Dimethylamineborane                                                                            4.2 × 10.sup..sup.-2 M                                 HCO.sub.2 Na     5 × 10.sup..sup.-1 M                                   pH               4.5                                                          Temperature      60.0°C                                                % P              9.90                                                         % B              0.19                                                         Example 6                                                                     ______________________________________                                        Ni               8.9 × 10.sup..sup.-2 M                                 NaH.sub.2 PO.sub.2                                                                             2.4 × 10.sup..sup.-1 M                                 Dimethylamineborane                                                                            1.3 × 10.sup..sup.-2 M                                 HCO.sub. 2 Na    5 × 10.sup..sup.-1 M                                   pH               5.5                                                          Temperature      60.0°C                                                % P              6.16                                                         % B              0.30                                                         Example 7                                                                     ______________________________________                                        Ni               8.9 × 10.sup..sup.-2 M                                 NaH.sub.2 PO.sub.2                                                                             2.4 × 10.sup..sup.-1 M                                 Dimethylamineborane                                                                            2.1 × 10.sup..sup.-2 M                                 HCO.sub.2 Na     5 × 10.sup..sup.-1 M                                   pH               5.0                                                          Temperature      60.0°C                                                % P              8.05                                                         % B              0.15                                                         Example 8                                                                     ______________________________________                                        Ni               8.9 × 10.sup..sup.-2 M                                 NaH.sub.2 PO.sub.2                                                                             2.4 × 10.sup..sup.-1 M                                 Dimethylamineborane                                                                            3.4 × 10.sup..sup.-2 M                                 HCO.sub.2 Na     5 × 10.sup..sup.-1 M                                   pH               4.5                                                          Temperature      60.0°C                                                % P              8.59                                                         % B              0.36                                                         Example 9                                                                     ______________________________________                                        Ni               8.9 × 10.sup..sup.-2 M                                 NaH.sub.2 PO.sub.2                                                                             2.4 × 10.sup..sup.-2 M                                 Dimethylamineborane                                                                            4.2 × 10.sup..sup.-2 M                                 HCO.sub.2 Na     5 × 10.sup..sup.-1 M                                   pH               4.0                                                          Temperature      60.0°C                                                % P              9.04                                                         % B              0.20                                                         ______________________________________                                    

I claim:
 1. A magnetic memory storage device comprising:a relativelythick rough substrate of a non-magnetic material that is heat resistantto a temperature of at least about 290° C., a relatively thick film of anon-magnetic alloy composed of about 0.1 to about 0.7 wt. % boron, about6 to about 16 wt. % phosphorus, and the balance nickel, on saidsubstrate, said film having a highly polished surface, a relatively thinfilm of a cobalt-phosphorous alloy magnetic material on said alloy film,and a thin film of a cobalt oxide protective material on said film ofmagnetic material.